import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.Iterator;
import java.util.Set;

/**
 * @author: zlz
 * @date: 2021/9/12 10:20
 * @description:
 * @since: JDK1.8
 */
public class NioWithSelector {
    public static void main(String[] args) throws Exception{
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.socket().bind(new InetSocketAddress(9000));
        serverSocketChannel.configureBlocking(false);
        Selector selector = Selector.open();
        // 把serverSocketChannel注册到selector上去
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println("服务启动成功");
        while (true) {
            // 阻塞等待需要处理的发生
            selector.select();
            // 获取selector中注册的全部事件的SelectionKey实例
            Set<SelectionKey> selectionKeys = selector.selectedKeys();
            Iterator<SelectionKey> iterator = selectionKeys.iterator();
            // 遍历SelectionKey对事件进行处理
            while (iterator.hasNext()) {
                SelectionKey key = iterator.next();
                // 如果是OP_ACCEPT事件，则进行连接获取和事件注册
                if(key.isAcceptable()) {
                    ServerSocketChannel server = (ServerSocketChannel)key.channel();
                    SocketChannel socketChannel = server.accept();
                    socketChannel.configureBlocking(false);
                    // 这里只注册了读事件，如果需要给客户端发送数据可以注册写事件
                    socketChannel.register(selector, SelectionKey.OP_READ);
                    System.out.println("客户端连接成功");

                } else if (key.isReadable()) {// 如果是读事件则进行读取和打印
                    SocketChannel socketChannel = (SocketChannel)key.channel();
                    ByteBuffer byteBuffer = ByteBuffer.allocate(128);
                    int len = socketChannel.read(byteBuffer);
                    if (len > 0) {
                        System.out.println("接收到消息:" + new String(byteBuffer.array()));
                    } else if (len == -1) {
                        System.out.println("客户端断开连接");
                        socketChannel.close();
                    }
                }
                // 从事件集合里删除本次处理的key,防止下次selector重复处理
                iterator.remove();
            }
        }

    }
}
